Dry-laid floors have been known for centuries and it is still common practice to lay wooden boards across joists to form such a floor.
Where a heavy load-bearing floor has been required, e.g. in factories, it has been common, however, to lay solid floors using wet concrete.
In more recent years, suspended floors have been laid on concrete or steel beams. A reinforced concrete raft is often cast in situ on such beams by means of shuttering laid between the beams. An example of a floor of this type is illustrated in U.K. Patent Specification No. 2053313. Parallel beams of inverted-T shape are provided and panels are laid between the beams, supported on the flanges defined by the cross-piece of the "T". Wet concrete is then laid on the panels and on the beams and allowed to set. The ends of the panels adjacent the beams are bevelled to form a triangular section gap between each end of each panel and the adjacent upright wall of the corresponding beam. This gap fills with concrete to form concrete columns along the beams to support the concrete raft.
In this prior art patent specification, the panels, which form shuttering, are left in situ and are made of material with good heat insulating properties, foamed polystyrene being preferred. The foamed polystyrene supports the unset concrete during construction of the floor, but has no supporting function in the completed floor. The set concrete shrinks away from the panels and the raft is wholly supported by the beams.
The contribution to the art provided by the published U.K. patent specification is an improvement in insulation effected by providing foamed polystyrene insulating members around the underside of the beams.
It is also common practice to provide dry-laid floors supported by beams. Slabs of concrete are dry-laid on the beams. Heat insulation in floors of this type has been provided by means of sheets of foamed polystyrene laid on the slabs and beams, with a surface covering of wooden sheets. The wooden sheets spread the load, in use, and avoid local damage to the polystyrene layer. The polystyrene layer is thin and has no supporting function.